Inventive concepts relate to semiconductor devices and more particularly, to semiconductor devices for automatically performing a calibration operation without an external zero-quotient (ZQ) calibration command and calibration methods thereof.
In general, various semiconductor devices formed of central processing units (CPUs), memories, and integrated circuits (ICs), such as gate arrays, are used for numerous digital apparatuses such as personal computers (PCs), servers, work stations, or the like. Mostly, the semiconductor devices include an input circuit for receiving signals from an external circuit via an input pad, and an output circuit for providing internal signals to the external circuit.
Meanwhile, due to an increase of operating speed of the digital apparatuses, a swing width of each of the signals that are interfaced between the semiconductor devices is reduced. The reduction of the swing width minimizes the transmission time of the signals. However, as the swing width is reduced, the semiconductor devices are affected by external noise, and signal reflection caused by an impedance mismatch is a serious problem in an interface.
The impedance mismatch occurs due to external noise, a change in a power voltage, variations in temperature, or a change in a semiconductor manufacture process. When the impedance mismatch occurs, it is difficult to rapidly transmit data, and output data from an output terminal of a semiconductor device can be distorted. Thus, a semiconductor device of an input apparatus may receive a distorted output signal. The distorted output signal often causes problems such as a set-up/hold failure, miss-calculation, or the like. In order to solve these problems, a semiconductor device, which is rapidly operated, uses an impedance mismatching circuit adjacent to a pad in an IC chip.
In general, for impedance mismatching between a transmitter and a receiver, a source termination is performed by an output circuit in the transmitter, and a parallel termination is performed by a termination circuit that is connected in parallel with an input circuit connected to an input pad in the receiver.
A process for providing pull-up and pull-down codes to terminations based on a process, voltage, and temperature (PVT) variation is related to ZQ calibration. A termination resistor of a data input/output pad (DQ pad) is controlled by using codes that are generated as a result of the ZQ calibration.
For example, the semiconductor device includes a ZQ pin as a terminal for the ZQ calibration, and thus receives ZQ calibration commands ZQCS (ZQ calibration short) and ZQCL (ZQ calibration long) from an external source. When the external ZQ calibration commands ZQCS and ZQCL are received, the ZQ calibration is performed in a period that is defined by the external ZQ calibration commands ZQCS and ZQCL. Since it is not possible to use the output circuit during the ZQ calibration, an access to the IC chip is prevented, and a next command is not input. The period defined by the external ZQ calibration commands ZQCS and ZQCL indicates a period for the ZQ calibration, and thus, the ZQ calibration needs to be completed within the predetermined period. The ZQ calibration is performed by matching the codes with an externally-mounted termination resistor.
Meanwhile, once the ZQ calibration is complete, an output impedance of the semiconductor device may be changed according to a circumstance in which the semiconductor device is disposed, e.g., an operation mode, a power voltage, a temperature, or the like.